Abstract: Secreted antibodies are a key player for exerting appropriate humoral immunity. For instance, in infectious diseases, poly-specific “natural” antibodies provide early protection, independent of T cell help. If this line of defense is crossed, T cell-dependent immune responses then generate a humoral memory provided by long-lived plasma cells secreting specific antibodies of adapted avidity and isotype. Secreted antibodies provide an efficient line of defense against re-infection and are backed up by specific memory B and T cells. In the field of humoral immunity, great discoveries including identification of a special T cell subset helping B cell activation (TFH), have been made in a last couple of years; however, important questions (such as mechanisms for affinity maturation of antibodies) still remain. [...]

Abstract: Here we review recombinant proteins with a capability for dual-targeting. These molecules address two different antigens on the same tumor cell and therefore are called “dual-targeting agents”. By virtue of binding a chosen pair of antigens on the malignant cell, preferential binding to antigen double-positive over single-positive cells can be achieved when both are present in the same environment. Therapeutic effects of such agents are based on different modes of action: (1) They can act as pro-apoptotic agents or by inhibiting pro-survival signals; (2) The dual recognition moiety can be fused to effector-domains, such as bacterial toxins or other drugs, leading to the generation of bispecific antibody-drug conjugates (ADCs); (3) Dual-targeting agents can further be used to redirect an effector-cell to the tumor. A new generation of scFv-derived fusion proteins are the tandem single chain triplebodies (sctbs), which carry two scFv binding sites for antigens on the tumor cell plus a third, specific for a trigger molecule on an effector cell. The ability of preferential or selective targeting of antigen double-positive over single-positive cells opens attractive new perspectives for the use of dual-targeting agents in cancer therapy, and possibly also for the treatment of certain inflammatory and autoimmune disorders.

Abstract: Bivalent single chain (sc)Fv-Fc antibodies have been used for years as recombinant alternatives of natural immunoglobulins. We have extended this approach to the scFv-Fc-scFv antibody format to obtain tetravalent antigen binding and the possibility to generate bispecific antibodies. We developed a mammalian expression vector system to construct tetravalent scFv-Fc-scFv antibodies with two NcoI+NotI compatible cloning sites flanking the Fc gene fragment. We demonstrated direct cloning from single chain antibody gene libraries and tested various scFv combinations. Transient production of scFv-Fc-scFv antibodies in human embryonic kidney (HEK) 293T cells achieved volumetric yields of up to 10 mg/L. However, expression levels were strongly dependent on the carboxyterminal scFv and the scFv combination. All scFv-Fc-scFv antibodies exclusively formed disulfide-linked homodimers. Antigen binding studies revealed dual specificity for all scFv-Fc-scFv employing different scFv fragments. Comparison of C-reactive protein (CRP) specific monovalent scFv LA13-IIE3, bivalent scFv-Fc and Fc-scFv LA13-IIE3, and tetravalent scFv-Fc-scFv (scFv LA13-IIE3 in combination with scFvs LA13-IIE3, TOB4-B11, or TOB5-D4) revealed an up to 500-fold increased antigen binding. This novel scFv-Fc-scFv antibody expression system allows simple and fast testing of various scFv combinations.

Abstract: Antibody-based immunotoxins comprise an important group in targeted cancer therapeutics. These chimeric proteins are a form of biological guided missiles that combine a targeting moiety with a potent effector molecule. The targeting moiety is mostly a monoclonal antibody (MAb) or a recombinant antibody-based fragment that confers target specificity to the immunotoxin. The effector domain is a potent protein toxin of bacterial or plant origin, which, following binding to the target cells, undergoes internalization and causes cell death. Over time and following research progression, immunotoxins become better fitted to their purpose, losing immunogenic fragments and non-specific targeting moieties. Many immunotoxins have gone through clinical evaluation. Some of these have been shown to be active and work is progressing with them in the form of further clinical trials. Others, mostly developed in the previous century, failed to generate a response in patients, or even caused undesired side effects. This article reviews the antibody and protein-toxin based immunotoxins that were clinically evaluated up to the present day.

Abstract: A number of cytokines have shown beneficial effects in preclinical animal models of cancer and chronic inflammatory diseases. However, cytokine treatment is often associated with severe side effects, which prevent the administration of clinically relevant doses in humans. Immunocytokines are a novel class of biopharmaceuticals, consisting of a cytokine moiety fused to monoclonal antibodies or to an antibody fragment, which selectively accumulate at the disease site and thereby enhance the therapeutic effects of cytokines. This review surveys the recent preclinical and clinical advances in the field, with a special focus on the impact of antibody formats, target antigen and cytokine moieties on the therapeutic performance in vivo. We also discuss emerging data about the possibility to combine immunocytokines with other pharmacological agents.

Abstract: Unmodified antibodies (abs) have been successful in the treatment of hematologic malignancies, but less so for the treatment of solid tumors. They trigger anti-tumor effects through their Fc-domains, and one way to improve their efficacy is to optimize their interaction with the effectors through Fc-engineering. Another way to empower abs is the design of bispecific abs and related fusion proteins allowing a narrower choice of effector cells. Here we review frequently chosen classes of effector cells, as well as common trigger molecules. Natural Killer (NK)- and T-cells are the most investigated populations in therapeutical approaches with bispecific agents until now. Catumaxomab, the first bispecific ab to receive drug approval, targets the tumor antigen Epithelial Cell Adhesion Molecule (EpCAM) and recruits T-cells via a binding site for the cell surface protein CD3. The next generation of recombinant ab-derivatives replaces the broadly reactive Fc-domain by a binding domain for a single selected trigger. Blinatumomab is the first clinically successful member of this class, targeting cancer cells via CD19 and engaging T-cells by CD3. Other investigators have developed related recombinant fusion proteins to recruit effectors, such as NK-cells and macrophages. The first such agents currently in preclinical and clinical development will be discussed.